Method for preparing alkali and heat stable polyols

ABSTRACT

The invention relates to a method for preparing alkali and heat stable polyols, whereby sugar alcohols are treated with reagents to obtain stabilised sugar alcohol syrups and the stabilised alcohol syrup is subjected to a purification step by passing the stabilized sugar alcohol syrup over at least one ion-exchanger resin, and the stabilized sugar alcohol syrup being purified by a double passage over a cationic anionic ion-exchanger configuration (CACA), comprising at least a first weak acidic cationic ion-exchanger resin and a second strong, medium or weak basic anionic ion-exchanger resin.

The invention relates to a method for preparing alkali and heat stablepolyols, in which sugar alcohols are treated with reagents to obtain astabilized sugar alcohol syrup by means of reagents and the stabilizedalcohol syrup is subjected to a purification stage by passing thestabilized sugar alcohol syrup over at least one ion-exchanger resin.

By polyols are meant sugar alcohol syrups, by which reference is made tothe hydrogenation products of polysaccharide hydrolysates, comprising,but not restricted to, hydrolysates obtained from starch, xylanes,arabinoxylanes, cellulose or other vegetal polysaccharides. Typicalstarch hydrolysates are, for instance, dextrose, high DE glucose syrups,high maltose syrups, standard glucose syrups and maltodextrines,including low DE maltodextrines.

Alkali and heat stability or sugar alcohols is important in a number ofindustrial and food applications, as shown in JP 63/079644 and EP 0 711743. The alkali and heat stability in these patent documents is obtainedby treating sugar alcohols by means of reagents in such a manner that asmuch colour forming components as possible are removed.

In JP 63/079844 sugar alcohol syrups are treated at a pH=9.5-13 at hightemperatures and during a period varying between 30 minutes and 2 hours.

In EP 0 711 743 stabilization is realized through a fermentation,oxidation or caramelisation stage.

The thus stabilized sugar alcohol syrup is then further subjected to apurification stage in order to obtain the final product.

In JP 63/079844 this purification stage comprises a treatment of thetreated syrup with ion exchanger resins. Here the syrup, which wascooled down to 50° C. was first passed over a strong acid cationicresin, then over a weak or medium base anionic resin and finally over amixed bed, composed of the same cationic and anionic resins as mentionedabove and in a 1:2-ratio. The temperature at which these resins wereused not being mentioned in this patent document.

In example 1 of EP 0 711 743, the stabilized syrup is purified by meansof a strong acidic cationic resin and a strong basic anionic resin. Herealso, no reference is made to any temperature at which these ionexchange resins are used.

In EP 1 095 925 an improved method is considered for purifying sugaralcohol syrups which were subjected to an alkali and heat stabilizationtreatment. In this method purification occurs by at least one passage ofthe stabilised sugar alcohol syrup over a strong acidic cationic resinat a temperature of below 50° C., in a preferred form of below 40° C.and in the most preferred form the temperature is situated between 20°C. and 30° C.

In EP 1 095 925 the importance of the working temperatures of resinswith respect to the level of reducing sugars desired after purificationis mentioned. From this it is apparent that working temperatures ofbelow 30° C. give cause for products having an excellent heat and alkalistability, such as required for a number of applications.

The temperature is the more important when the hydrolysable sugaralcohol content of the syrup, for instance, maltitol, maltotriitol andhydrogenated oligosaccharides, increases.

From U.S. Pat. No. 5,254,174 the importance of the working temperatureof strong acidic cationic resins with respect to the hydrolysis of thesubstrate treated, is considered. There, with respect to theoligosaccharide treatment, it is suggested to use the strong acidiccationic resins at temperatures situated between 25° C. and 35° C., inorder to prevent hydrolysis of the oligosaccharides.

In U.S. Pat. No. 4,029,183 is considered how the inversion reaction ofsucrose during decationization, is prevented by controlling thetemperature of the strong acidic cationic resin between 25° C. and 30°C.

The use of strong acidic cationic resins during the refining ofstabilised sugar alcohol syrups, however, has the disadvantage that,when products having a low reducing sugar content are needed, it isnecessary to work at temperatures between 20° C. and 30° C. In order tocool down the syrups to these relatively low temperatures, additionalcooling equipment and energy has to be used. As a consequence of theselower temperatures, the viscosity of these relatively concentratedsyrups increases, because of which treatment is further complicated(pressure build-up in resins). This is more especially the case withsyrups obtained through hydrogenation of, among others, starchhydrolysates that are mainly composed of di-, tri- and higheroligosaccharides (for instance, medium and high maltose syrups,maltodextrines). Another disadvantage of strong acidic resins is relatedto the fact that a large excess of acid is required in order toregenerate these resins.

In EP 0 262 711 the use of a combination of weak acidic cationic andweak or medium basic anionic resin is considered for purification ofbeet sugar thin juice.

It should be noted that this method aims at a partial demineralisationof beet sugar thin juice (as described in the examples). However, fromthese examples it becomes clear that the removal of cations and colouris far from complete.

The object of the invention is to provide for a method for preparingalkali and heat stable polyols not showing the disadvantages mentionedabove.

This object is obtained by providing a method for preparing alkali andheat stable polyols, in which:

-   -   sugar alcohols are treated by means of reagents to yield a        stabilized sugar alcohol syrup, and    -   the stabilized sugar alcohol syrup is subjected to a        purification stage by passing the stabilized sugar alcohol syrup        over at least one ion-exchanger resin,        and in which the stabilized sugar alcohol syrup is purified by        means of a double passage over a cationic anionic ion-exchanger        configuration (CACA), comprising at least a first weak acid        cation ion-exchanger resin and a second strong, medium or weak        base anion ion-exchanger resin.

In a preferred method according to the invention a temperature is usedvarying between 20° C. and 60° C.

In a preferred method, according to the invention, the CACAconfiguration uses a “merry-go-round” system, comprising at least 3pairs of columns, each pair of columns consisting of a column filledwith cationic ion-exchanger resin and a column filled with anionicion-exchanger resin. At least two pairs of columns are used for thepurification of the stabilised sugar alcohol syrup, while at least athird pair of columns is regenerated.

Such a system has the advantage that the refining of the stabilisedsugar alcohol syrup may be done in a continuous manner.

In a specific preferred method according to the invention said cationicion-exchanger resin in the column is built-up of two layers, the layerof ion-exchanger resin at the exit of the column consisting of a strongacidic ion-exchanger resin.

In a more specific method according to the invention said strong acidicion-exchanger resin represents 0.5% to 50% of the volume of the cationicion-exchanger resin in the column.

In a still more specific method according to the invention said layer ofstrong acidic ion-exchanger resin represents 5% to 25% of the volume ofthe cationic resin in the column.

In a preferred method of the invention a temperature is used varyingbetween 30° C. and 50° C.

In a specific preferred method according to the invention a temperatureis used varying between 35° C. and 45° C.

In a particular method according to the invention the treatment of thesugar alcohols in order to obtain a stabilized sugar alcohol syrup, in afirst stage comprises a hydrogenation of a corresponding polysaccharidehydrolysate to yield a hydrogenated sugar alcohol syrup, after which analkali and heat treatment of the hydrogenated syrup is carried out inorder to obtain said stabilized sugar alcohol syrup.

In a more particular method according to the invention the hydrogenatingreaction is interrupted when the residual reducing sugars dry weightcontent drops below 0.2%.

In a most particular method according to the invention the hydrogenatingreaction is interrupted when the residual reducing sugars dry weightcontent drops below 0.1%.

In an advantageous method according to the invention the conductivity ofthe refined sugar alcohol syrups amounts to less than 1% of the originalconductivity.

In a more advantageous method according to the invention theconductivity of the refined sugar alcohol syrups amounts to less than0.5% of the original conductivity.

Preferably, in the method according to the invention, sugar alcohols areused which, after hydrolysis, contain a total reducing sugar content,varying between 3.5% and 96%, as determined by means of Bertrand'smethod.

More preferably, in the method according to the invention, sugaralcohols are used which, after hydrolysis, contain a total reducingsugar content, varying between 40% and 95%, as determined by means ofBertrand's method.

Most preferably, in the method according to the invention, sugaralcohols are used which, after hydrolysis, contain a total reducingsugar content, varying between 50% and 92%, as determined by means ofBertrand's method.

In a preferred method according to the invention, said sugar alcoholsare obtained by hydrogenation of medium to high maltose syrups.

The characteristics and particularities of the present invention arefurther explained hereafter on the basis of an implemented example, withreference to the drawing enclosed. It should be noted that specificaspects of this example are described as a preferred example only ofwhat is meant in the scope of the general description of the inventionmentioned above and on no account may be interpreted as a restriction ofthe scope of the invention as such and as expressed in the followingclaims.

In the drawing enclosed, FIG. 1 is a schematic representation of a“merry-go-round” system according to the invention.

The method according to the invention, in a first stage comprises ahydrogenation of a corresponding polysaccharide hydrolysate (likewisecalled sugar alcohol), then an alkali and heat treatment of thehydrogenated sugar alcohol syrup in order to obtain a stabilized sugaralcohol syrup, and finally the purification or the refining of thestabilized sugar alcohol syrup, after which a sugar alcohol syrup isobtained which is alkali and heat resistant.

The method according to the invention is advantageous for sugar alcoholsyrups containing a total reducing sugar content, after hydrolysis,varying between 3.5 and 98%, as determined by means of Bertrand'smethod. Further, it was also found, that this method also yields verygood results when treating sugar alcohol syrups containing a totalreducing sugar content, after hydrolysis, lying between 40% and 95%,preferably between 50 and 92%, as determined by means of Bertrand'smethod. Similar typical sugar alcohol syrups, such as mentioned above,are obtained through hydrogenation of medium to high maltose syrups.

The hydrogenation is carried out with the help of methods that aregenerally known in the state or the art. The hydrogenation isinterrupted when the residual reducing sugar dry weight content dropsbelow 0.2%, preferably below 0.1%.

The hydrogenated sugar alcohol syrup is then subjected to an alkali andheat treatment, in order to obtain a stabilised sugar alcohol syrup, thestabilised sugar alcohol syrup undergoing a colouration during thisprocess.

In a next step, this stabilised sugar alcohol syrup is purified orrefined, in order to remove the colour components present. Thepurification stage consists of a double passage (CACA) over a cationicanionic (CA) ion-exchanger configuration. In the process, use is made ofa weak acidic cationic resin and a strong, medium or weak basic anionicresin, this at a temperature situated between 20° C. and 60° C., and ina still more preferred method the temperature varies between 30° C. and50° C., and in a still more preferred method, between 35° C. and 45° C.

It is thereby of the utmost importance that after the CACA treatment thesyrups are substantially entirely demineralised and colourless.Moreover, these syrups should remain substantially colourless, whensubjected to an additional alkali and heat treatment.

In an advantageous method the CACA configuration is used in a“merry-go-round” system, as shown in FIG. 1. A similar system consistsof 3 pairs of columns (or a plurality of them), each pair of columnsconsisting of a column filled with cationic resin and a column filledwith anionic resin. Moreover two pairs of columns are used for purifyingthe treated syrup (CACA), while the third pair of columns isregenerated. The refined syrup is then collected after having passed thesecond set of CA-columns. Thus, when the first pair of columns getsexhausted, the supply is changed over to the second pair of columns andthe refined syrup is then collected after the third set of CA-columns.At the same time the first set of resins is then sweetened off andregenerated.

In a variant of a method according to the invention, the cationic resinin the column is built-up of two layers, the layer of resin at the exitof the column consisting of a strong acidic cationic resin. This layerrepresents 0.5% to 50% of the volume of cationic resin, preferablybetween 5% and 25%.

After treatment, the conductivity of the refined sugar alcohol syrupsamounts to less than 1%, preferably leas than 0.5% of the originalconductivity.

The sugar alcohol syrups obtained by means of the method according tothe invention are most suitable for preparing products with an alkalinepH, or products containing an alkaline component, or which are treatedor obtained through a heat treatment.

Hereafter, the invention will be further explained by means of a numberof examples, which, however, should by no means be interpreted as arestriction of the scope of the invention as such and as expressed inthe adjacent claims.

EXAMPLE 1

A high maltose syrup is hydrogenated according to standard proceduresuntil the residual reducing sugar dry weight content is below 0.2%.

The hydrogenated syrup (about 50% d.w.), having a composition asindicated below, is then subjected to an alkali and heat treatment, thesyrup being brought to a pH=11, and then heated during 2 hours at 100°C.

The composition of the syrup is as follows (dry weight %) Sorbitol 6.5%Maltitol 62.5% Maltotriitol 18.5% Higher DP polyols 12.4%After the alkaline heat treatment, the hydrogenated syrup is cooled downto a temperature situated between 35° C. and 40° C., and subjected to apurification step by means of ion-exchangers. The system is composed ofthree pairs of columns. Each pair consists of a column filled with acationic resin and a column filled with an anionic resin.

The cationic resin used is a weak acidic cationic resin (Lewatit S8528)and the anionic resin is a strong basic resin (Lewatit OC1074). Theresins are filled into double-walled glass columns having an internaldiameter of 25 mm. The volume of the resin amounts to 100 ml of LewatitS8528 and to 100 ml of Lewatit OC1704. The columns are heated to 35° C.and the velocity of flow is 200 ml/hour.

The supply to the first pair of columns was stopped after 3100 ml syruphad been treated by this first pair of columns (stage 1). Supply wasthen changed over to the second pair of columns, which before had beenused as “finishing” pair.

The third pair of columns is now turned on as a “finishing” pair, whilethe first pair is sweetened off and regenerated (stage 2). Then thesupply of this second pair of columns is stopped again after 3100 ml andsupply is changed over to the third pair of columns (stage 3). In thismanner operation continues in a “merry-go-round” configuration, alwaysone pair of columns being regenerated, next to the CACA-refining systemwhich is still operating. The refined syrup is collected at the exit ofthe second pair of columns of the CACA-configuration.

The extinction value of the non-refined substrate treated, beforeCACA-treatment, amounts to 2.45 (1 cm cuvette, 420 mm).

After CACA-treatment during the first stage, the syrup thus refined issubjected to an alkali and heat stability test.

This test, called the S-test, is described in detail in EP711743. Anincreased stability of the sugar alcohol is reflected by low extinctionvalues, as determined with this S-test (preferably <0.1).

The extinction value (S-value) of the sugar alcohol syrup mentionedabove, after refining, was determined on the syrups collected during thefirst, second and third stage, as shown in FIG. 1. CACA-treatmentS-value Stage 1 0.055 Stage 2 0.052 Stage 3 0.051

COMPARATIVE EXAMPLE 1

The malitol syrup of example 1 was subjected to an ion-exchangerpurification stage, making use of the following combinations of resins:

-   (A) CA: strong acidic—medium basic (Dowex CM15 and Purolite A847S)-   (B) CA: strong acidic—strong basic (Dowex CM15 and Lewatit OC1074)

Moreover, the purification stage was carried out at two differenttemperatures; 23° C. and 35° C.

In the table below, the S-values of the syrups thus treated are comparedto the S-values of the products obtained by the method according to theinvention. Example 1 (A)23° C. (A)35° C. (B)23° C. (B)35° C. S-value0.051 0.089 0.095 0.075 0.085

It may be concluded that the results obtained by the CACA-treatmentaccording to the invention are permanently better than those obtained bythe methods known already.

EXAMPLE 2

The maltitol syrup used in example 1 was subjected to an ion-exchangerpurification stage, making use of a “merry-go-round” CACA-system, asdescribed in example 1, the cationic resin in the column being composedof a layered bed of 90 ml weak acidic cationic resin (IMAC HP336) on topof a layer of 10 ml strong acidic cationic resin (Dowex CM15). Theanionic resin is a medium basic resin (Purolite A847S).

The maltitol syrup of example 1 is refined over equal volumes ofcationic and anionic resins at 35° C. The refined syrup has an S-valueof 0.063.

1. Method for preparing alkali and heat stable polyols, in which: sugaralcohols are treated with reagents to obtain a stabilized sugar alcoholsyrup, and the stabilized sugar alcohol syrup is subjected to apurification stage by passing a stabilized sugar alcohol syrup over atleast one ion-exchanger resin, wherein the stabilized sugar alcoholsyrup is purified by a double passage over an cationic anionicion-exchanger configuration (CACA), comprising at least a first weakacidic cationic ion-exchanger resin and a second strong, medium or weakbasic anionic ion-exchanger resin.
 2. Method according to claim 1,wherein a temperature is used varying between 20° C. and 60° C. 3.Method according to claim 1 or 2, wherein the CACA configuration uses a“merry-go-round” system, comprising at least 3 pairs of columns, eachpair of columns consisting of a column filled with cationicion-exchanger resin and a column filled with anionic ion-exchangerresin, and at least two pair of columns being used to purify thestabilized sugar alcohol syrup, while at least a third pair of columnsis regenerated.
 4. Method according to claim 3, wherein said cationicion-exchanger resin in the column is built-up of two layers, the layerof ion-exchanger resin at the exit of the column consisting of a strongacidic ion-exchanger resin.
 5. Method according to claim 4, wherein saidlayer of strong acidic ion-exchanger resin represents 0.5% to 50% of thevolume of the cationic ion-exchanger resin in the column.
 6. Methodaccording to claim 5, wherein said layer of strong acidic ion-exchangerresin represents 5% to 25% of the volume of the cationic resin in thecolumn.
 7. Method according to claim 2, wherein a temperature is usedwhich varies between 30° C. and 50° C.
 8. Method according to claim 2,wherein a temperature is used which varies between 35° C. and 45° C. 9.Method according to claim 1, wherein the treatment of sugar alcohol inorder to obtain a stabilized sugar alcohol syrup in a first stagecomprises a hydrogenation of a corresponding polysaccharide hydrolysateto yield a hydrogenated sugar alcohol syrup, after which an alkali andheat treatment of the hydrogenated syrup is carried out in order toobtain said stabilized sugar alcohol syrup.
 10. Method according toclaim 9, wherein the hydrogenation reaction is interrupted when theresidual reducing sugar dry weight content drops below 0.2%.
 11. Methodaccording to claim 9, wherein the hydrogenation reaction is interruptedwhen the residual reducing sugar dry weight content drops below 0.1%.12. Method according to claim 1, wherein the conductivity of the refinedsugar alcohol syrups is less than 1% of the original conductivity. 13.Method according to claim 1, wherein the conductivity of the refinedsugar alcohol syrups is less than 0.5% of the original conductivity. 14.Method according to claim 1, wherein sugar alcohols are used which,after hydrolysis, contain a total reduced sugar content, varying between3.5% and 98%, as determined by means of Bertrand's method.
 15. Methodaccording to claim 1, wherein sugar alcohols are used which, afterhydrolysis, contain a total reduced sugar content, varying between 40%and 95%, as determined by means of Bertrand's method.
 16. Methodaccording to claim 1, wherein sugar alcohols are used which, afterhydrolysis, contain a total reduced sugar content, varying between 50%and 92%, as determined by means of Bertrand's method.
 17. Methodaccording to claim 14, wherein sugar alcohols are obtained throughhydrogenation of medium to high maltose syrups.